The root canal procedure is a well-known endodontic therapy for the treatment of pulp necrosis and for the retreatment of previously obturated canals that have failed. The procedure generally includes removing at least a portion of the tooth crown to expose the canal system, followed by the extraction of the contents from the one or more canals of the tooth. The canals are then generally subjected to mechanical shaping operations, such as reaming or filing in order to reduce and/or remove various irregularities within the canal, and to prepare the canal to receive a filling material. While the canals are shaped, the canals are regularly cleaned with a variety of solutions to remove material dislodged by the shaping operations, and to prepare the canals to receive a filling material. The filling material is generally tightly packed into the canals to form a seal within the canals to prevent leakage into the canal spaces. An additional filling material is then generally placed in the crown opening. Alternatively, a replacement crown may be affixed to the tooth to complete the procedure.
In most instances, complete obturation of the canals is complicated by the internal shape of the canals. The canals are generally curved, and often have an irregular cross sectional area along the length of the canal. Additionally, the canals frequently have lateral fissures, or passages, that radiate outwardly from the interior of the canal. Accordingly, the filling material and the method used to obturate the canals must be capable of adequately conforming to the curved and/or irregular shape of the canals, and to substantially fill and seal the canals, including the lateral fissures, if the therapy is to be successful.
One prior art endodontic technique employs silver points in conjunction with a sealer to obturate the canal passage. The silver point is a relatively slender and slightly tapered metal insert that, when properly positioned in the canal, extends to the foramen at the apical tip of the root. Since the silver point generally has a diameter that is much less than the diameter of the canal, the sealer is employed solely to fill the space between the silver point and the interior surface of the canal. The sealer is a relatively viscous semi-fluid material that does not chemically interact with either the silver point or the tooth material and does not form an adhesive bond with the silver point or the surrounding tooth material. Instead, the sealer serves as an interface material between the canal wall and the silver point to prevent the migration of liquid substances along the interface region between the tooth and the silver point.
Although the silver point technique is relatively simple and may be relatively quickly administered, a principal disadvantage is that the silver point does not adequately “cork” the apical foramen to create the desired seal. Further, the technique generally cannot subject the relatively viscous sealer material to sufficient hydrostatic pressure to ensure that all of the irregular spaces and lateral fissures in the interface region are sufficiently filled, since the sealer is generally incapable of adequately migrating into either the irregular spaces, or the minute lateral fissures or accessory canals that radiate outwardly from the root canal passage. Consequently, the use of silver points in root canal therapy exhibits a relatively high degree of failure, which often necessitates the retreatment of the affected tooth.
Various other prior art endodontic techniques use an elastic material, called gutta percha, as the filling material. Gutta percha is a natural rubber material that is semi-rigid at room temperatures that becomes plastic, or semi-liquid upon heating. The gutta percha material is generally formed into relatively long and slender tapered points that may be introduced into the root canal by either a vertical condensation or a lateral condensation method.
In the vertical condensation method, the gutta percha point is introduced into the canal with a relatively viscous sealer applied to the inner surfaces of the canal. The point is heated and a relatively small amount of gutta percha is removed from the canal leaving a softened portion of gutta percha within the canal. This portion is subjected to vertical compression by a tool called a plugger to form a relatively densely compressed mass within the canal of the tooth. The process of heating the point, removing a small portion, and condensing the remaining portion is repeated two or more times. This technique thus subjects the gutta percha material to significant hydrostatic pressure, which forces the sealer and the softened gutta percha into the small irregularities and accessory canals found within the root. The condensing process is complete when the apical three to five millimeters of the canal is sealed with thermally softened gutta percha that conforms to the irregular shape of the canal. The next step is to “back fill” the remaining unfilled portion of the canal. One common method to accomplish the backfilling procedure is to inject warm gutta percha material into the canal with a “gutta percha gun” such as the Obtura II system, available from Spartan/Obtura Inc. of Fenton, Mo. According to this method, a gutta percha pellet is inserted into the gun and heated to a predetermined temperature. The thermally softened gutta percha is expressed in small increments into the canal through a narrow tip of the gun starting at the most recently condensed portion of gutta percha. Vertical condensation then proceeds by compressing the material with the plugger to compact the gutta percha while it is cooling. The process of expressing a small amount of gutta percha into the canal followed by vertical compaction is repeated until the canal is filled to the desired length.
An alternative method for obturating the canal space that entails fewer steps and less equipment than the foregoing method is to utilize a commercially-available gutta percha carrier unit. The unit comprises an elongated, axisymmetric plastic portion having a small handle at one end, and a mass of gutta percha disposed on an opposing end that extends along a portion of the length of the plastic portion. In this method, the operator places a sealer into the canal and, while holding the handle of the unit, heats the gutta percha on the carrier to soften it. The gutta percha disposed on the unit is then introduced into the canal. The portion of the carrier protruding from the tooth is then removed and the root canal procedure is complete.
In the lateral condensation method, a main gutta percha point is introduced into the root canal, followed by the successive introduction of additional points surrounding the main point until the root canal is completely filled. As in vertical condensation, a sealer is used to provide a relatively fluid impermeable interface between the tooth and the gutta percha material.
Although the foregoing techniques constitute a substantial improvement over the silver point technique, numerous drawbacks still exist. For example, the introduction of gutta percha points into the canal, either by the vertical or lateral condensation methods discussed above, is generally time consuming, and requires a high degree of skill to ensure that the therapy is successful. For example, in the vertical condensation method, the force applied to the material must be sufficient to create sufficient hydrostatic force to compress the gutta percha and sealer into all of the internal spaces in the canal. However, the application of excessive force to the gutta percha may cause the tooth to be inadvertently fractured, or otherwise damaged. In addition, the application of excessive force to the gutta percha material may cause the material, or the sealer to be extruded through the apical foramen and into the surrounding tissue to form an impacted mass of material that may lead to localized irritation, or even inflammation of the periapical tissue. Still further, the viscous sealer employed is generally unable to fully migrate into minute fissures, or to chemically bond with the tooth or the filler material, as discussed above.
Although using the gutta percha carrier unit, as discussed more fully above, has greatly simplified the process of obturating the root canal, there are additional drawbacks associated with this method. With the vertical or lateral condensation techniques, the main or master cone can be trimmed to size or chemically softened for proper seating and then radiographed while lodged in the canal to verify that the canal is properly filled. This pre-fitting procedure is accomplished prior to the actual obturation process, but cannot be performed with the carrier technique. Consequently, the operator usually has a single opportunity to heat the gutta percha on the carrier and insert it into the canal in an attempt to properly seat the gutta percha to the desired length. Further, when retreatment of a root canal is required where the canal has been previously obturated with a carrier unit, the retreatment is more difficult due to the presence of the plastic carrier, which causes the material to be more difficult to remove, since the carrier unit may not dissolve in any of the conventional solvents typically used to remove root canal filling materials. Accordingly, a significant amount of time may be expended by the operator in removing and repairing the failed treatment.
Although the use of gutta percha has greatly improved the success rate of endodontic treatment, this success relies on the ability of gutta percha to mechanically “plug” the various openings of the canal, since the sealer does not provide bonding or chemo-mechanical adherence between the tooth material and the gutta percha material.
Chemical bonding agents have been successfully used in general dentistry for a number of years to bond composite and porcelain restorations onto and into teeth. Studies have shown that when such bonding agents are used as filling materials to seal the coronal portion of canals filled with gutta percha, the bonded area is impervious to leakage. Accordingly, there is a need in the art for an apparatus and method for obturating the canal utilizing a similar bonding agent that will greatly improve the seal of the canal while generally reducing the time and the relatively high degree of skill required to perform the procedure.